T0521—2005Mixing and on-site sampling methods for cement concrete mixtures

1Purpose, scope of application, and reference standards

This method specifies the indoor mixing and on-site sampling methods for cement concrete mixtures.

This method is applicable to the mixing and on-site sampling of ordinary cement concrete,It is also applicable to the mixing and on-site sampling of other special cement concrete such as lightweight water mixed concrete, waterproof cement concrete, and rolled cement concrete,But due to its particularity, there are special requirements for instruments and methods,All should be carried out in accordance with the relevant technical regulations for cement concrete.

Reference standards:

Concrete testing mixer(JG244)

Vibration table for concrete testingJGT245

2Instruments and materials

21forced mixer:Should comply with the current "Concrete Testing Mixer(JG244)The regulations

22vibration table:Should comply with the current "Vibration Table for Concrete Testing"JGT245The regulations

23scale:The maximum range is not less than50kg,Sensitivity not greater than5g

24balance:The maximum range is not less than2000The sensitivity is not greater than1g

25other:Iron plates, shovels, etc

3Mixing steps

31Maintain room temperature during mixing20℃±5℃,Relative humidity greater than50Pn

32Before mixing,The material should be placed at a temperature of20℃45Indoor temperature of ℃,And the time is not less than the axish

33To prevent segregation of coarse aggregates,Aggregate can be stacked in different grades,During the entire process from sampling to the end of the test, the sample is mixed in a certain proportion when in use,Avoid direct sunlight and moisture evaporation,Protective measures should be taken when necessary

34The total amount of the mixture should be at least more than the required amount20%The above. The material for mixing concrete is measured by mass,Accuracy of weighing:Aggregate for Shi%,水、水泥,Admixtures and additives are0.5%

35Both coarse and fine aggregates are in a dry state(Moisture content less than0.5%The fine aggregate and moisture content are less than0.2%Coarse aggregate)As a benchmark,When calculating water consumption, the moisture content of coarse and fine aggregates should be deducted

3.6Addition of admixtures

(1)For additives that are insoluble or difficult to dissolve in water and do not contain deliquescent salts,It should be mixed with a portion of cement first,To ensure dispersion

(2)For additives that are insoluble in water or difficult to dissolve in water but contain deliquescent salts,It should be mixed with fine aggregate first

(3)For water-soluble or liquid additives,It should be mixed evenly with water first

(4)Other special additives,It should still comply with the relevant standards.

3.7Various tools used for mixing concrete,Such as iron plates, shovels, and spatulas,It should be pre wetted with water,After use, it must be cleaned

wash sth. clean.

3.8Before using the blender,A small amount of mortar should be used to rinse the chamber first,Scrape out the mortar from the lake chamber again,To avoid the loss of cement mortar adhesion to the cylinder wall during formal concrete mixing. Water cement ratio and sand cement ratio of chamber mortar,It should be the same as the formal concrete mix proportion.

3.9When mixing with a mixer,The mixing amount should be the maximum capacity of the mixer14-34

3.10The mixer is used to mix and weigh the raw materials according to regulations,Add coarse aggregate, fine aggregate, and cement in sequence into the mixer. Start the mixer,Mix the materials evenly,Slowly add water during the mixing process,The total feeding time should not exceed2minAfter adding all the water,Continue mixing about2min,Then pour the mixture onto an iron plate,Further manual mixing1-2mm,Be sure to make the mixture uniform and consistent

3.11Manual mixing:When using manual mixing,Wet the iron plate and shovel with a damp cloth first,Mix the weighed sand and cement evenly on an iron plate,Add coarse aggregate,Mix and stir evenly. Then pile up this mixture into long piles,Center digging long groove,Pour the weighed water into about half,Carefully mix it with the mixture,Stack the materials into a long pile again,Dig into a long groove,Pour in the remaining water,Continue mixing,Stir back and forth at least10throughout

312From the completion of sample preparation to the start of various performance tests, it should not exceed5mn(Excluding molded specimens)

4on-site sampling

41On site sampling of fresh concrete:When taking representative samples of fresh concrete from mixers, hoppers, transport carts, and poured components,Representative samples of approximately equal quantity must be taken from three or more different locations(Do not extract concrete that has already separated),Use an iron shovel indoors to roll and drop evenly,Then immediately conduct a test on the mixture,The sampling amount of the mixture should be more than the required quantity for the test15times,And the minimum volume should not be less than20L.

42From the first sampling to the last sampling,Should not exceed15min

provisions explanation

The performance of cement concrete composites is closely related to the well and process,To standardize the sampling of indoor squeezed and water mixed concrete aggregates and on-site concrete aggregates,Develop this method specifically. Due to the fact that the calculation of the mix proportion is based on the original solution's dry state,so,The raw materials should be measured in advance